1. Field of the Invention
The present invention relates to a steering system for a boat with three or more propulsion units arranged side-by-side.
2. Description of the Related Art
Conventional boats may have three propulsion units arranged side-by-side. The propulsion units may be outboard motors, stern drives or inboard-outdrive engines. Each propulsion unit has an associated shift lever and throttle lever. To control the boat, the operator individually operates all six shift and throttle levers.
More recently, steering systems for multi-engine boats have included only two levers. An operator performs shift and throttle operations for all the three propulsion units via the two levers (see, for example, Japanese Patent Abstracts JP-A-2006-29183 and JP-A-2006-35884).
Japanese Patent Abstract JP-A-2006-29183 describes a steering system that has two control levers for a boat having three propulsion units. To facilitate low speed operation, an operator can hold the two control levers at a predetermined position in a neutral range to independently throttle the middle propulsion unit. With the control levers in this position, the two outer propulsion units are idling. The boat can thus move at a very slow speed via operation of only two levers.
Japanese Patent Abstract JP-A-2006-35884 describes a steering system that has two control levers for a boat having three propulsion units. The steering system includes an imaginary lever associated with the middle propulsion unit. The position of the imaginary lever is determined based on the detected positions of the two levers. The operator can thus perform shift and throttle operation for the three propulsion units through the use of only two levers.
In the steering systems above, an operator can throttle the boat to move at a very slow speed. If one of the propulsion units stops, the operator must first return the two levers to the neutral position and turn the start switch to on to restart the propulsion units. However, if the failure occurred in the propulsion unit, the propulsion unit will not restart. The operator then must turn off the main switch associated with the failed propulsion unit and tilt the propulsion unit up to use the two remaining propulsion units to return to port. Unfortunately, the operator cannot predict which of the three propulsion units may fail and how the failure will impact control of the boat.